1. Field of the Invention
The invention relates to an injection valve with a pump piston.
2. Description of the Prior Art
Injection valves with a pump piston to raise the pressure of the injected fluid are used, for example, in automobile engineering to achieve particularly high injection pressures. In modern common-rail injection systems, for example, diesel fuel is injected into the combustion chamber of an internal-combustion engine at a pressure of up to 2000 bar.
A fuel injection system for internal combustion engines by which fuel is fed from a high-pressure accumulator to an injection valve is known from U.S. Pat. No. 5,413,076. The fuel is fed into a pump chamber which is delimited by one face of a pump piston. A second face of the pump piston delimits a booster chamber, which contains an injection needle. This injection needle is preloaded against the sealing seat, so that in its closed position the booster chamber is isolated from the spray holes. The injection needle is linked to a second piston, which delimits a control chamber. This control chamber is linked to a 3/2-way valve by a bore hole. The 3/2-way valve is in turn connected to a high-pressure accumulator by a second line, and via a third tube to a discharge line. The positional setting of the 3/2-way valve determines a predefinable pressure setting for the control chamber, and this controls the position of the injection needle. An additional controllable valve is provided between the high-pressure accumulator and the pump chamber, and this links the high-pressure chamber to the pump chamber as determined by the positional setting of the controllable valve. Control of the injection process is exercised by the positional settings of the 3/2-way valve and the additional valve.